Analysis for quantifying microscopic diffusion anisotropy

Abstract

A method for MRI includes performing an MRI experiment on a material to acquire an echo attenuation data set using a gradient modulation scheme comprising 1D diffusion encoding and to acquire an echo attenuation data set using a gradient modulation scheme comprising 2D diffusion encoding, determining respective first-order deviations μ2 from mono-exponential decay in said echo attenuation data sets, and generating MRI parameter maps or MR image contrast based on said first-order deviations μ2.

The invention claimed is: 
     
       1. A method for MRI, the method comprising:
 performing an MRI experiment on a material to acquire an echo attenuation data set using a gradient modulation scheme comprising 1D diffusion encoding and to acquire an echo attenuation data set using a gradient modulation scheme comprising 2D diffusion encoding; 
 determining respective first-order deviations μ 2  from mono-exponential decay in said echo attenuation data sets; and 
 generating MRI parameter maps or MR image contrast based on said first-order deviations μ 2 . 
 
     
     
       2. The method according to  claim 1 , wherein
 the 1D diffusion encoding includes diffusion encoding along a single encoding gradient direction, and 
 the 2D diffusion encoding includes diffusion encoding along two orthogonal encoding gradient directions. 
 
     
     
       3. The method according to  claim 2 , wherein
 the 1D diffusion encoding forms part of a single PGSE sequence, and 
 the 2D diffusion encoding forms part of a double PGSE sequence. 
 
     
     
       4. The method according to  claim 2 , wherein each of the acquired echo attenuation data sets includes signal intensities averaged across multiple encoding directions. 
     
     
       5. The method according to  claim 1 , wherein each first order deviation μ 2  corresponds to a second central moment of a distribution of diffusion coefficients for the respective echo attenuation data sets. 
     
     
       6. The method according to  claim 1 , wherein the parameter maps or MR image contrast is generated based on a difference between said first-order deviations μ 2 . 
     
     
       7. The method according to  claim 6 , wherein the parameter maps or MR image contrast is generated based on a mean diffusivity and a difference between said first-order deviations μ 2 . 
     
     
       8. The method according to  claim 1 , further comprising:
 fitting respective fitting functions to the echo attenuation data sets using the first order deviations μ 2  as respective fit parameters. 
 
     
     
       9. A method for MRI, the method comprising:
 performing an MRI experiment on a material to acquire an echo attenuation data set using a gradient modulation scheme comprising anisotropic diffusion encoding and to acquire an echo attenuation data set using a gradient modulation scheme comprising isotropic diffusion encoding; 
 determining respective first-order deviations μ 2  and μ 2   iso  from mono-exponential decay in said echo attenuation data sets; and 
 generating MRI parameter maps or MR image contrast based on said first-order deviations μ 2  and μ 2   iso . 
 
     
     
       10. The method according to  claim 9 , wherein the anisotropic diffusion encoding includes
 1D diffusion encoding including diffusion encoding along a single encoding gradient direction, or 
 2D diffusion encoding including diffusion encoding along two orthogonal encoding gradient directions. 
 
     
     
       11. The method according to  claim 10 , wherein
 the 1D diffusion encoding forms part of a single PGSE sequence, or 
 the 2D diffusion encoding forms part of a double PGSE sequence. 
 
     
     
       12. The method according to  claim 9 , wherein the acquired echo attenuation data set acquired using a gradient modulation scheme comprising anisotropic diffusion encoding includes signal intensities averaged across multiple encoding directions. 
     
     
       13. The method according to  claim 9 , wherein each first order deviation μ 2  and μ 2   iso  corresponds to a second central moment of a distribution of diffusion coefficients for the respective echo attenuation data sets. 
     
     
       14. The method according to  claim 9 , wherein the parameter maps or MR image contrast is generated based on a difference between said first-order deviations μ 2  and μ 2   iso . 
     
     
       15. The method according to  claim 9 , wherein the parameter maps or MR image contrast is generated based on a mean diffusivity and a difference between said first-order deviations μ 2  and μ 2   iso . 
     
     
       16. The method according to  claim 9 , further comprising:
 fitting respective fitting functions to the echo attenuation data sets using μ 2  and μ 2   iso  as respective fit parameters.